Squishband

Hi guys & gals, I'm having a very specific problem that I'd appreciate someone with good tech / tuning / trouble shooting experience to chime in...reward for the one(s) who can solve my RX8's problem. In short form: The engine will not hold idle once it leaves the cold start circuit. Here are the specifics on the vehicle. 04' 6spMT USDM VIN#JM1FE173140103144 61Kchassis / 250miles on rebuilt motor. All Atkins components, tight side of spec, current compression is ~100psi @ 250rpm, +/- 2psi across all 6 chugs. not quite broke in yet. Header no a/p, No Cat, RB back, Takeda intake tube 3.4"ID. All new oem ignition components, battery and Altn. 2-stroke inj system. I think that covers it. So I can start the car cold no problem, it fires right up. After a few moments on warm up circuit the idle fades down, then it seems the ignition just shuts down. A similar sound like coming to a stop in gear and turning the key off at the last few seconds, it makes a flat "jake brake" diesel type intake sound. Now here is the interesting part. If I try to restart the engine on the key, it just cranks quite fast, almost wanting to run @ idle speed but will not fully ignite to get off the starter. BUT if I get out and give it a slight roll to jump start it in 1st gear, the motor will fire right up with barely even one or two compression chugs. I'm not using the key starter here, just let the clutch out and away it goes. (really slow crank speed ~50 to 100rpms, below stall speed). Any questions so far?
I got the car as a basket case, so I've been going back over all the details. This weekend, I removed the MAF sensor to clean the "wire" but it was very clean and didn't make any difference. However, i noticed it is a Toyota p/n#22204-22010 Denso brand#197400-2030. I looked up the Denso # for RX8's and it should be a #197-6020. Obvious reaction would be to buy the exact part number, but it's a $130 special order and I'm not keen on part swapping just to see. Any one have Denso specific knowledge about those numbers? Also, I'm slowly going through the Cobb tuning process with MM, but would like to sort this bug out before proceeding. I'd really appreciate good sound tech help please, save the negative comments, bs or ill advice. BTW, I cnc my own version of injection bypass for anyone that can help sort out this problem with me. Much thanks in advance!

dannobre

iTrader: (3)

Have you checked the throttle body? The DBW throttle is responsible for the idle circuit...and if it isn't working properly then it won't idle

Is there any porting done to the motor at all??

What are the STFT when it idles?

Sure you don't have a Vac leak?..or the injectors wired wrong?

Brettus

iTrader: (2)

If you could check afrs and stft/ltft at idle that might give you a clue ....

HiFlite999

iTrader: (2)

The too large intake tube will cause the engine to run leaner than stock, assuming the stock MAF sensor. With some random sensor, who knows what's happening. Are the screens in place? If not, low speed fueling, especially with a short ram, will be a mess.

Harlan

iTrader: (3)

If it's a similar hot wire maf then you should be able to cal it with an accessport. It would be nice to have a starting point though. Try to find a voltage/flow curve for that maf.
Also the reason it starts at all is because the ecu doesn't use the maf for fueling while starting.

j9fd3s

on the MAF front there are actually two, from the start of production to 2006? the MAF was a ZL01-13-215, which looks to be 197400-2010

sometime in 06, they changed it to an L321-13-215, which looks to be Denso part number 197400-2240

i'm not sure what the difference is, Mazda superseded the ZL01 with the L321, and if you order a ZL01, you'd get an L321.

so since these seem like they are also used on toyotas, and interchangeable, it might be a better idea to look at a scanner. you should look and see what idle air flow should be, i wanna say 4-6, but i'm not sure about the units

nycgps

iTrader: (1)

wow u guys are really nuts, i stop reading after the first 10 words...

Squishband

Hey Thanks for all the good insight. I'll try to dig into it some more today. The MAF tube has no screen and it's not perfectly round either. Although it seems to work out to the same area based on inside circumference. I'm going to try and track down a stock tube and MAF sensor to see if that helps. Although, I believe the car ran with this setup before I got it, so that's what has me stumped. On the TB, how does the idle circuit work? Is it a bypass port around the throttle plate?
Thanks guys!

TeamRX8

iTrader: (25)

{ FS } Used Air Flow Sensor (MAF) P/N ZL01-13-215 - RX8Club.com

Cliffjumper126

You could always buy one from somewhere like advance auto (where I got mine a couple months ago, actually says Toyota lol, works like a charm though) and return it if it doesn't fix anything. I paid like $90 for mine

Squishband

Ok Guys, Sorry for the long pause. A friend stopped over with his 04' RX8 and we swapped his stock intake tube, MAF and airbox setup with mine. Well his ran fine and mine still would not idle when it fell off the cold circuit. We also swapped TB's with no difference. Sorry I can't get any clear stft/ltft or afrs at idle because I have to blip the throttle to keep it alive.... Back to your thoughts.
It starts and runs fine on a cold circuit, but once it idles long enough to transition to a regular warm idle the motor just shuts down. So my next thought is to pull the intake and inspect the injector wiring. When the car is started cold, it does not use the MAF, so it has a dedicated setting for fuel and ignition correct? Then it transitions to reading the MAF and O2 sensors right? What else changes in that transition. Do the inner and outer injectors vary in that transition? Would this glitch be something that could be detected in the Cobb tuning process? It doesn't seem like MM has noticed that the motor has an idle issue in my downloads, but maybe the data doesn't show it?

j9fd3s

i think you can eliminate the TB/MAF/air box from your search.

it should have a sub 2000rpm fuel trim, oui?

i suspect a vacuum leak first maybe, but on the FD's we used to see the CAS wires get cooked, and they would work with the engine cold and go open with it hot, the FD has two, and would usually throw a code.

that is speculation on your part. i think once its running it uses the MAF, although under 65c coolant temp it will either run in open loop, and or run richer.

i don't actually know, but it would seem like the target AFR's change, and maybe the 02 sensors switch on, if they aren't already.

Squishband

I've got some more data for you. First off, I've gone all through the lines and intake connections, and to the best of my ability, it does not have a vacuum leak. I even introduced a little leak to see if that had any effect...nothing. And, gone as far as using some O-ring gel seal on all the intake connections. So, I went out on a long easy drive and managed to capture a few moments of idle before and after. In a semi cold state the MAF was reading 5/6 on an idle of about ~1100rpm, stft was neg 24-22. Warm engine MAF was still reading 5 on a ~900rpm, stft neg 14-16. The idle tends to wander a little so those values are constantly fluctuating, but I'm trying to give you an average. Plus I've got to stab the throttle when the idle falls off then stft goes into the + range then settles back to negative. There is no CEL or codes, I've checked. I could post a short video of the intake setup and running idle if anyone is interested...it might help?
On the injector wiring, all have Black and Black/Wht stripe. Then the colors on each going across are are Green, White, Yellow/Green, Blue/White. I'm searching for the wiring diag, if anyone has a link please chime in. Thank Again!

j9fd3s

a MAF value of 5@900rpm is about right. a negative STFT (what is the LTFT?) means that the ECU thinks the engine is rich, so its pulling fuel.

what happens if you unplug the o2 sensors and reset the ECU, so it stays @0 fuel trims?

Squishband

J9 the ltft seems to hoover at -0 or -1. I didn't spend much time watching that because I have a short window of idle time. Also, I notice that when I gently bring the motor down to idle I can get it to settle around 850rpms and the stft will focus in on -10 to -14 but as it starts to wonder around it appears the motor will just shut down when the stft falls below -10. Like someone turned the key off. Could that be a weak fuel pump? I also tried with a charger hooked up to the battery just to see if I had a low voltage issue pump / injectors / ignition...no change.

When driving, if I lift off the throttle to slow or down shift it seems to cut the ignition off. Then there is a pause followed by a backfire, when I go back to throttle or try to blip for down shift. It's definitly an on/off/on feel, rather then stumbling or random misfire.

I can try unplugging the O2 sensors & reset to see what happens.

Charles, I would be much obliged if you could post the injector wiring too!

roflcopter

iTrader: (2)

Your fuel trims seem strange to me, I'm pretty sure it shouldn't be pulling THAT much fuel except for off throttle deceleration, but definitely not at idle, I could be wrong though.

My suggestion... are you sure the resistor for the fuel pump(located on the bracket for the AIR pump assembly) is still there and functional? I'm willing to bet that it is failed somehow and while the car uses the full voltage straight to the fuel pump(on throttle and during warm up) it runs fine but once it gets to where it should pass voltage through the resistor(such is warm idle and cruise) there is no power to the fuel pump.

If not that, I would look at FPR issues as I believe your issue is definitely one of fueling.

stinksause

iTrader: (5)

did you reset the ECU when swapping the intake?

Squishband

Hey guys, thanks for all the input...I spent some time looking over several wiring diagrams and discovered some differences in the wire color callouts. Anyway, it was my error, I had two injectors switched. I discovered that at some point there were different shades of blue or (Lavinder) I guess I should have smelled the wires to be sure LOL! Thanks for the support, another 8 back on the road!